Radio beacon keying circuit



"March 8, 1949. .s. B. WHITE RADIO BEACON KEYING CIRCUIT 2 Sheets-Sheet 1 Filed Dec. 15, 1944 S. B. WHITE arch 8, 1949.

RADIO BEACON KEYING CIRCUIT 2 Sheets-Sheet 2 Filed D90. 15, 1944 INVENTOR. dm/wzyfi 144 7:5

BY 71 f w Patented Mar. 8, 1949 RADIO BEACON KEYING CIRCUIT Stanley B. White, Dayton, Ohio Application December 15, 1944, Serial No. 568,371

4 Claims.

(Granted under the act of amended April 30, 1928;

The invention described herein may be manufactured and used by or for Government for governmental purposes, without the payment to me of any royalty thereon.

The present invention relates to improvements in automatic miniature radio range transmitting equipment of the character such as disclosed in United States Patent No. 2,352,216, granted to Melvin and White June 27, 1944, and particularly relates to means for eliminating key clicks and keying transients to thereby improve signal characteristics and reception.

It is well known that opening and closing a keying circuit of a radio transmitter produces shock excitation which produces transient oscillations which are audible in a receiver as a click or thump. Various means such as filter circuits and inductive time lag circuits are generally employed to eliminate these objectionable oscillations in commercial radio communication equip ment. In miniature radio range equipment the problem of eliminating key click is much more difiicult than in conventional radio transmitting equipment due to the receiving antenna being in such close proximity to the transmitter. Further the phasing of adjacent antennas 180 apart renders it possible to eliminate key clicks in only two of the four signal quadrants. A further difficulty arises from the fact that in the On course signal zones a continuous signal must be heard and hence the amount of time delay which can be employed to minimize shock .excitation of the transmitter due to keying is distinctly limited because a slow decay of sa the A signal and a slow build-up of the N signal will cause a pronounced gap to be produced between the signals in the out-of-phase quadrant of the range.

The object of the invention is to eliminate key clicks and shock excitation phenomena from miniature radio range transmitting equipment and to produce clear signals in all of the range signal quadrants. These objects are attained in accordance with the present invention by a combination of features such as keying the grid circuit of keying tubes by grid blocking; phasing adjacent transmitting antennas 90 apart; employing noninductive time delay circuits to eliminate a considerable part of the keying transients and employing degeneration to remove the remaining transients and smooth out any humps or ripples in the transmitted signals. The manner in which these features cooperate will be apparent by reference to the detailed description hereinafter given and to the in "which:

l "is a view showing the transmitter assembly .as employed to set up a radio range for use in conjunction with an aviation ground trainer and;

appended drawings 1 March 3, 1883, as 3-70 0. G. 757) Fig. 2 is a circuit diagram of the transmitter of Fig. 1 embodying the features of the invention and;

Fig. 3 is a schematic diagram illustrating the eiiects of key click suppression where adjacent antennas are phased 130 apart and;

Fig. 4 is a view illustrating the effect of phasing the adjacent antennas 90 apart in accordance with the invention.

Referring now to Fig. 1, the reference numeral l generally indicates a table or instructors desk having a top surface .2 on which is placed a conventional radio range chart C and supporting a power-propelled recorder 3 having a marker wheel t and driving wheels 5 driven by electric motors 5. The Wheels 4 and 5 are steerable and interconnected by gearing (not shown) adapted to be actuated by an electric self-synchronous repeater or receiver S1, electrically connected by a conductor S2 to a corresponding transmitter unit S3 positioned in the base of an aviation round trainer 8 and actuated by gearin such that rotation of the trainer causes a corresponding change in the heading of the recorder 3.

The trainer 8 has a conventional radio receiver H3 mounted-in the cockpit thereof to which is connected a conventional headset !2 worn by the trainer occupant. The receiver H] in connected by means of a shielded conductor l3 to a receiving antenna f4 mounted as at 15 on the recorder 3 so that the axis of the antenna is coincident with the steering axis of marker wheel 4.

A transmitting antenna array generally indicated by reference numeral 20 is positioned over the table surface 2 such that the apex of the array is approximately 17 inches above the top of the recorder 3 and the vertical axis of the array is directly over the radio range station point on the radio range chart C on the table top 2 and upon which the recorder leaves its trace.

The antenna array includes an insulating supporting rod 2!, .adjustably clamped as at .22 at the outer end of a tubular support 23 which overlies the table surface and has a vertical por, tion 24 extending down and secured to the table A. Four triangular plates 23 of insulating material are each provided with hinge portions 29 for adjustable rotation about the axis of rod 2| to vary the angular relation of the antennas and thus vary the angular relation of the on-course signal legs. A disc 13! provided with a suitable azimuth scaleserves to indicate the adjusted position of the plates 28.

Metal antenna rods indicated respectively by numerals 32, 33, 34, and 35 are secured to the hypotenuse of each of the plates 28 so that the rods lie in the common surface of an inverted cone having its vertex on the axis of rod 2|. Shielded antenna conductors are connected to the outer ends of the .antenna rods, the conductors indicated by numerals 36 to 39 inclusive are connected to a radio transmitter unit generally indicated at 40. The structure so far described, with the exception of the mounting of the transmitting antenna above the table and the mounting of the receiving antenna on the upper side of the recorder, is similar to the arrangement disclosed in the aforementioned Patent 2,352,216. The mounting of the transmitting antenna array above the trainer desk or table and mounting the pick-up antenna above the recorder does away with any disturbing effects due to the presence of the recorder in the signal field since the portion of the field traversed by the pick-up will be unaffected by the presence of the recorder.

The novel features incorporated in the transmitter to avoid key clicks will now be described.

Referring to Fig. 2, the transmitter 40 includes a radio-frequency oscillator 4|, an audio-frequency oscillator 42 and radioand audio-frequency amplifiers 43 and 44 respectively coupled in an oscillator circuit to a tank coil 45 in a manner similar to that disclosed in the aforementioned Patent No. 2,352,216 and operative such that a 450 kilocycle radio-frequency carrier wave is modulated at an audio-frequency of 1020 cycles to give an audible tone. The modulated radio-frequency output of the tank coil 45 is inductively transmitted to a coupling coil 46 which has one of its terminals connected by means of a conductor 4'! and condenser C1 to the grid of a keyer and amplifier tube V1. The other terminal of the coupling inductance 4B is connected by means of a conductor 48 and condenser C2 to the grid of a second keyer and amplifier tube V2. The plates of the tubes V1 and V2 are connected by means of conductors 49 and 50 respectively to load resisters R and R6 and are also connected to antenna coupling condensers C: and Ca respectively. The coupling condenser C7 feeds the signal output in the plate circuit of tube V1 into the primary coils 53 and 54 of a pair of antenna coupling transformers, the secondary coils 55 and 56 of which respectively feed the antenna rods 32 and 33 through antenna conductors 26 and 31. The inner terminals of the coupling transformers are connected into a common ground. Similarly coupling condenser Cs feeds the output in the plate circuit of tube V2 to the primary coils 51 and 58 of a second pair of antenna coupling transformers, the secondary coils 59 and 60 of which are respectively connected to antenna rods 34 and 35 by means of antenna conductors 38 and 39. The coupling transformers are all variable in inductance so that voltage fed to the respective antenna rods may be varied in the same manner as in the aforementioned Melvin and White Patent No. 2,352,216.

A resister R3 and condenser C3 are connected in series across conductors 41 and 48 ahead of coupling condensers C1 and C2 and are of such value as to constitute a 90 phase shifting network whereby the signals appearing on the grid of one of the tubes will be 90 out of phase with respect to the signals appearing on the grid of the other tube. The purpose of the plase shifting network will be later described.

The cathodes of tubes V1 and V2 are connected together and also connected by means of a conductor 6! to an unbypassed resistance R4 which is connected at a common point 62 between resister R3 and condenser C3. A conductor 63 connected at the common point 62 is connected at point 64 to a voltage divider comprising resistances R7 and Rs which divide the voltage between 3+ and ground to apply a potential such as 20 volts to conductor 63. Resistance R1 is bypassed by means of a condenser C1.

The connection point 64 between resistances R1 and R8 is connected by means of conductor 65 to a switch arm 66 of an AN signal keyer having a central contact 61 thereon adapted to engage either of the pair of contacts 68 and 69 and the contact arm 66 being actuated by means of a well known A-N type of signal cam III. The signal cam 10 is of the same character as generally employed in miniature radio range signal apparatus to key the transmitter output to give the conventional A and N radio range signals. The upper contact 69 is connected to the upper switch contact 12 of a conventional A signal switching mechanism which includes a central contact 13 mounted on a switch arm I4 and adapted to engage the upper contact I2 or a lower contact 16 as determined by cam 15. The lower contact 16 of the A signal switch is connected to the lower contact ll of a similar N signal switch and each of which are adapted to be connected to identification signal keyers (not shown) well known in the art, the switches being operative to connect the A-N signal keyer to the keyer tubes and periodically connect the identification signal keyers in place of the A-N keyer.

The N signal switching cam mechanism includes a central contact mounted on a pivoted switch arm 8| and adapted to engage either lower contact 'l'I or an upper contact 82 as determined by a switching cam 18 in a manner well known in the art. Lower contact 68 of the A-N signal keyer is connected by means of conductor 83 to the upper contact 82 of the N signal switch device and the contact arms 14 and BI of the A and N signal switching devices are respectively connected to conductors 85 and 86. Conductor 85 is connected through resistances R9, R10, and R11 to the grid conductor 48 of keyer tube V2 and conductor 86 is connected by means of resistances R12, R13, and R11 to the grid conductor 41 of keyer tube V1.

The B+ voltage appearing in the plate circuit of tubes V1 and V2 by means of conductor 5| is also applied by means of a conductor 81 across resistances R15 and R16 to ground and a conductor 88 connected so as to divide the voltage across resistances R15 and R16 is connected to a switch arm 90 having a contact 9! thereon adapted to engage a contact 92 as determined by a cam 93. A conductor 95 conducts current from switch contacts 9|-92 when the latter are closed directly to the cathodes of tubes V1 and V2 to provide the proper cathode bias when identification signals are being transmitted as will be hereinafter explained.

Operation When the radio-frequency oscillator 4| and audio-frequency oscillator 42 and their associated amplifiers are in operation, a continuous signal of 450' kilocy-cles modulated with an audio tone of 1020 cycles will appear in the tank coil 45 and also appear by inductive coupling in the inductance 46. Due to the phase shifting network comprising resistance R3 and condenser C3, the signal fed to one grid if allowed to pass would be 90 out of phase with the signal fed to the other grid of the respective keyer tubes V1 and V2. As previously noted in the description of Fig. 2,

the voltage divider comprising resistances Rv-Ra provides a voltage in conductor 53 which applied to the connection point 62 provides a fixed grid bias potential. Due to the connection of point 62 to the cathode circuit, the bypass condenser C4 provides a path for alternating current to round. However the resistance R4, which is in the cathode circuit and connected to the input circuit at point 62, is not bypassed, so that when tube V1 is operating the signal voltage appearing on the grid of tube V1 is the vector sum of the voltages across resistances R3 and R4 respectively. Since the output voltage appearing in the plate to cathode circuit of the tube will be substantially 180 out or phase with the input voltage, the voltage across the resistance R4 will be 180 out of phase with the incoming signal voltage appearing across resistance R3 and degenerative or negative feedback occurs. A similar action takes place when tube V2 is operating and tube V1 is cut oil, since then the voltage appearing on the grid of tube V2 is the vector sum of the input voltage appearing across condenser Ca and the feedback voltage across resistance R4, which voltages also will differ in phase by 180. While the degenerative or negative feedback reduces the output signal, it will also improve the signal to noise ratio and serves to partially eliminate the transients since it has the efiect of opposing fluctuations of voltage and tends to make the signal volume level constant. The common point of connection 62 between resistor R3 and condenser C3 is placed at a positive potential due to the voltage dividing arrangement consisting of resistance R7 and R8, the latter of which is connected to the B+ supply. This voltage is conducted through resistance R4 and causes both of the tubes V1 and V2 to be biased to cut ofi in the event that the A-N signal key contact 6'! is in the neutral position between key contacts 67 and B8.

A time delay circuit is provided for each of the kcyer tubes V1 and V2 and comprising condenser C1 and resistance R14 in the case of tube V1 and condenser C2 and resistance R11 in the case of tube V2. The time delay characteristics of these circuits are so chosen that the slope of signal build-up and signal decay curves are nearly alike so as not to produce distortion. The time delay circuits prevent the sudden build-up of potential on the grids of tube V1 and V2 respectively and also prevent abrupt cut-off and hence serve to eliminate a substantial portion of the transients produced by opening and closing of the A-N signal keying contacts 5?, B8, and 69, and that portion Of the transient oscillations which may not be eliminated by the time delay circuits are eliminated due to the degeneration produced in the cathode circuit by means of the unbypassed resistance R4.

When the respective A signal and N signal cams I5 and 18 are at their high points, the contacts 12 and 73 of the A signal and contacts 80 and 82 of the N signal switching mechanisms are respectively engaged, so that the A-N signal keyer device, actuated by cam 10, is rendered operative to apply a voltage from the end connection point or tap 64 and conductor 65 to either of the conductors 85 and 86 to alternately render the voltage on the grids of the tubes V1 and V2 sufliciently positive that the tubes will draw current and pass the keyed signal alternately into the plate circuits of the tubes to appear as N- signals on the antenna rods 32 and 33, and as A- signals on antenna rods 34 and 35.

In operation, the A-'-N signal cam"!!! is rotated continuously by means of a keyer motor not shown and periodically the switch cam's l5 and T8 are rotated so that grid conductors and 8B are disconnected from the A-N signal keyer and connected to identification signal keyers of "a type well known in the art so that identification signals will alternately appear in the radio range signal quadrants.

The antennas 32 and 33 or N signal antennas are arranged so as to 'be 180 out of phase with respect to each other and a similar condition prevails between antennas 34 and 35 which transmit the A signals, but due to the phase shifting network R3 C3, the signals in adjacent antennas will be out of phase so that if the time delay and degeneration are effective to eliminate key clicks, chirps and pops in one signal quadrant the same effect will be produced in all other signal quadrants, as distinct from the conventional phasing of between adjacent-antennas as heretofore employed. This will be more clear by reference to Figs. 3 and 4. As seen in Fig. 3, the solid line a represents, for example, an A signal envelope which dies away after cut-01f along the dotted line b-c and similarly the N signal builds up along dotted line de to the full line I representing the maximum voltage of the N signal. If the voltages are in phase in two of the signal quadrants when successive signals appear, the voltages will add so that the signals will blend together with no apparent gap and in such signal quadrant no key clicks would be heard, however, in the opposite quadrants, which are 180 out of phase, the signals will cancel and leave a gap between points b and e which will be readily audible in the car as an interruption of a continuous oncourse signal.

In accordance with the present invention as indicated in Fig. 4, with the voltages in adjacent antennas 90 out of phase, the signals on an oncourse signal leg between an adjacent pair of antennas may cut-01f and build up in the manner previously indicated but with the efiect that the voltages will tend to build up slightly at the point of cross-over, as indicated by the dotted lines, however, the eifect of degeneration will immediately tend to reduce such a signal peak to nearly a constant signal so that no interruption will be heard between the consecutive A-N signals in the on-course signal zones and this same condition will prevail in all of the signal quadrants and hence elimination of key clicks in one quadrant will serve to eliminate the same in all quadrants.

It has also been found that with a 90 phase difference in the signals between adjacent antennas the adjustment of the time delay circuits is much less critical than with conventional 180 phasing.

With the blocked grid keying as employed with the present invention, when the transmitter is sending A-N signals, the tubes V1 and V2 are always alternately operated, but when identification signals are being transmitted, there is a possibility of the 1020 cycle audio signal being heard in the background between identification signals, and to prevent this condition, the bias voltage from conductor 88 is applied to the oathodes of the tubes by means of switch 90, which is rendered operative whenever A-N switching devices are in a position to connect the identification signal keyers, and this insures sufi'lcicnt bias on the nonoperating tube to prevent any background signals being transmitted thereto during the operation of the other tube in transmitting other identification signals.

Having now described my invention, what I wish to secure by Letters Patent is:

I claim:

1. In an automatic miniature radio range device for radiating a radio range signal field over the surface of a recorder table of an aviation ground training device, the combination of a transmitting antenna array positioned over the table, said array including a plurality of antenna rods inclined to the vertical and forming two related pairs, the antenna rods of each pair being electrically phased at 180 with respect to each other, a radio signal generating transmitter unit connected to said antenna pairs, said transmitter unit including a radio-frequency oscillator, an audio-frequency oscillator, an output circuit fed by said oscillators with a modulated radio frequency current, a pair of keying tubes in said circuit and having the grids thereof connected in said circuit and normally biased to cut-off, keying means for selectively varying the grid potential on said keyer tubes to cause the same to pass a signal, a phase shifting network adapted to shift the phase of the signal voltages on said grids by 90 with respect to each other, time delay means associated with each respective grid for limiting the rate of signal build up and decay, and a connection between the plate circuit of each keyer tube and a respective one of said antenna pairs.

2. In an automatic miniature radio range device for radiating a radio range signal field over the surface of a recorder table of an aviation ground training device, the combination of a transmitting antenna array including a plurality of antenna rods forming two related pairs, the rods of each pair being electrically phased 180 apart with respect to each other, a transmitter unit having a pair of keyer tubes in the output circuits thereof, grid blocking keying means associated with said tubes to alternately render the same operative to pass a signal, means associated with the grid circuit of one of said keyer tubes to shift the phase of the signal current passed by said tube electrical degrees with respect to the signal current passed by the other of said tubes, and means for connecting the output circuit of each of said keyer tubes to a respective pair of said antenna rods.

3. The structure as claimed in claim 2 in which time delay means are provided associated with said grid blocking keying means to control the rate of signal build up and decay.

4. The structure as claimed in claim 2, in which time delay means are provided associated with said grid blocking keying means to control the rate of signal build-up and decay, and inverse feedback means associated with said keyer tubes to eliminate any residual keying transients not removed by the time delay means.

STANLEY B. WHITE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,960,350 Shackleton May 29, 1934 2,153,986 Mac Laren Apr. 11, 1939 2,312,962 De Florez Mar. 2, 1943 2,352,216 Melvin June 27, 1944 2,359,294 Blenman Oct. 3, 1944 2,366,603 Dehmel Jan. 2, 1945 2,435,502 Lang Feb. 3, 1948 2,444,477 Stout et al June 6, 1948 

